1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a printer, or a facsimile machine, which includes a developing apparatus using a toner and conducts image forming operations by an electrophotographic method or the like; a control system for the image forming apparatus; a cartridge; and a memory device mounted in the cartridge.
2. Related Background Art
In an image forming apparatus, such as a copying machine or a printer, an electrophotographic photosensitive member functioning as an image bearing member is charged by a charging apparatus and exposed by an exposure apparatus to form an electrostatic latent image, according to image information, on the surface of the electrophotographic photosensitive member, and the formed electrostatic latent image is developed by a developing apparatus to visualize it as a developer image. Then, the developer image is transferred to a transfer material, such as a sheet, by a transfer apparatus, this toner image is fixed on the transfer material by a fixing apparatus, and the transfer material is discharged.
As the above-mentioned developing apparatus of the image forming apparatus, for example, a two-component developing apparatus (hereinafter referred to as a developing apparatus) 101, for conducting developing using a two-component developer (hereinafter referred to as a developer) t containing a non-magnetic toner and a magnetic carrier as shown in FIG. 10, can be used.
The developing apparatus 101 includes a developing sleeve 103, which is located opposite to a photosensitive drum 100, functioning as an image bearing member, in an opening portion of a developing container 102 and rotatable in the direction of an arrow adjacent developing sleeve 103 in FIG. 10 (counterclockwise direction), a magnet roller 104 fixedly located in the developing sleeve 103, a developer regulating blade 105 for regulating the layer thickness of the developer t borne on the developing sleeve 103, agitating screws 106a and 106b for agitating the developer t contained in the developing container 102 and feeding it in the developing-sleeve side, a toner replenishing container 107 in which a toner is contained, a replenishing screw 109 for replenishing toner from the toner replenishing container 107 into the developing container 102 through a toner replenishing port 108, and an inductance sensor 110 for measuring the density of the developer t in the developing container 102.
The agitating screws 106a and 106b are located in substantially parallel to and along an inner wall 111, functioning as a partition plate. The inner wall does not exist in both longitudinal end portions of the agitating screws 106a and 106b, and these longitudinal end portions communicate with each other through communication portions (not shown). When the developing sleeve 103 is rotated, the developer t is circulated by the rotated agitating screws 106a and 106b through the communication portions of both sides of the inner wall 111 so that it is borne on the developing sleeve 103. The developer t is composed by mixing a non-magnetic toner particle and a magnetic carrier particle.
Next, a developing process of visualizing an electrostatic latent image formed on the photosensitive drum 100 by a two-component magnetic-brush method using the above-mentioned developing apparatus 101 and a circulating system for the developer t will be described. Note that a voltage having a predetermined polarity is applied to the photosensitive drum 100 and a voltage having a predetermined polarity is applied to the developing sleeve 103.
With respect to the developer t in the developing container 102, a developer is drawn to an N2 pole of the magnet roller 104 in accordance with agitating and feeding by the agitating screws 106a and 106b rotated according to the rotation of the developing sleeve 103. The developer is regulated by the developer regulating blade 105 located perpendicular to the developing sleeve 103 through a process in which it is fed from an S2 pole to an N1 pole. Thus, the developer is formed as a thin layer on the developing sleeve 103. When the developer formed as the thin layer here is fed to an S1 pole as a developing main pole, a magnetic brush is produced by magnetic force. The electrostatic latent image on the photosensitive drum 100 is reversal-developed by the developer, which stands like the ears of rice. After that, the developer t on the developing sleeve 103 is returned into the developing container 102 by a repulsive magnetic field of an N3 pole and that of the N2 pole and agitated by the agitating screws 106a and 106b. 
Further, the developer t in the developing container 102 is composed of a non-magnetic toner and a magnetic carrier and the magnetic permeability of the developer t is determined according to the carrier amount occupied per predetermined volume. Thus, when the magnetic permeability of the developer t is measured by the inductance sensor 110, the ratio between the toner and the carrier (hereinafter referred to as the toner density) can be detected.
Therefore, in the case where the toner density of the developer t is reduced according to the consumption of toner during developing, the reduced toner-density amount is measured at a time when the developer t fed by the agitating screw 106b transmits through the inductance sensor 110. The measurement information is outputted to a toner-replenishing control apparatus 112. As described below in detail, the toner replenishing control apparatus 112 causes the replenishing screw 109 to operate based on the measurement information inputted from the inductance sensor 110 so that the necessary toner amount is replenished from the toner replenishing container 107 into the developing container 102 through the toner replenishing port 108. Thus, the toner density of the developer t in the developing container 102 is always kept constant.
Note that, for example, optical-type density-detecting means can be used as means for detecting the toner density in the developing container 102 in addition to using the inductance sensor 110.
As shown in FIG. 11, in the toner-replenishing control apparatus 112 as the conventional example described above, a measurement value of the inductance sensor 110 corresponding to a predetermined toner density is used as a density standard value (toner-density standard value) 113 of the developing apparatus 101 so that a predetermined value is stored. At the time of toner-density control during an image forming operation, a signal (density measurement information) from the inductance sensor 110 is compared with the above-mentioned density standard value 113 by a comparison circuit 114 of the toner-replenishing control apparatus 112, the shift amount of current toner density with respect to the toner density of a standard developer is determined, and the consumed toner amount, that is, the replenishing toner amount a is calculated.
The toner in the toner replenishing container 107 is replenished into the developing container 102 through the toner replenishing port 108 according to the rotation of the replenishing screw 109. The toner amount fed at a time when the replenishing screw 109 is rotated one turn (replenishing amount per one rotation by screw) b is stored in advance in the toner-replenishing control apparatus 112. Thus, at the time of toner density control during an image forming operation, a screw rotation number c as a value obtained by dividing the above calculated replenishing toner amount a by the toner amount fed at a time when the replenishing screw 109 is rotated one turn (replenishing amount per one rotation by screw) b is calculated. The replenishing screw 109 is rotated by the calculated screw rotation number c to replenish the toner.
Now, in the toner replenishing operation by the control of the conventional toner replenishing control apparatus 112 as described above, the replenishing screw 109 is rotated by an amount proportional to the calculated replenishing toner amount a. Thus, there is a case where the following inconvenience is caused.
In the conventional toner replenishing operation as described above, the toner amount fed according to the rotation of the replenishing screw 109 actually has no proportional relationship with the rotation number of the replenishing screw 109. This is because the fed toner cannot follow the rotation of the replenishing screw 109 in the case where the replenishing screw 109 is rotated a large number of turns.
Thus, the feeding toner amount, which is actually replenished into the developing container 102 according to the screw rotation number c of the replenishing screw 109, which is determined by the above-mentioned conventional method, is shifted with respect to the calculated replenishing toner amount a so that the toner density in the developing container 102 is unstable. Therefore, in the worst case, fog on an image due to under-agitating of the developer t resulting from over-replenishing of the toner is caused or a reduction in image density resulting from a shortage of the toner replenishing amount is caused.
FIG. 12 shows, in the conventional toner replenishing operation as described above, the actual relationship between the rotation number of the replenishing screw 109 and the replenished toner amount (A in the drawing) and the relationship in the case where it is assumed that the rotation number of the replenishing screw 109 and the replenished toner amount have a proportional relationship (B in the drawing).
As shown by A in FIG. 12, up to now, with respect to the toner amount actually fed according to the rotation of the replenishing screw 109, the toner replenishing amount per one rotation tends to decrease as the rotation number of the replenishing screw 109 increases. Thus, in the case where the required toner replenishing amount is large, that is, in the case where the rotation number of the replenishing screw 109 becomes larger, the toner replenishing amount becomes insufficient.
Therefore, an object of the present invention is to provide an image forming apparatus capable of always replenishing the suitable amount of toner even in the case where a developing operation is conducted in which the replenishing toner amount required according to the measured density of the toner is large.